1. Field of the Invention
The present invention relates to an inter-frequency handoff execution method and apparatus in a mobile communication system, and more particularly, to an inter-frequency handoff execution method and apparatus in a code division multiple access(hereinafter, referred to as xe2x80x9cCDMAxe2x80x9d) cellular telephone system which transmits/receives data between a mobile terminal having a single radio frequency(RF) receiver and a base station and at the same time, searches the frequency supplied in other base station to thereby determine whether or not handoff is executed.
2. Discussion of Related Art
In configuration, generally, a cellular telephone system is comprised of a plurality of cells which are made by dividing the whole service area into a plurality of small areas in consideration of topographical characteristics and propagation environments, a base station which is placed in a preset service area and has a function of interfacing a mobile terminal to a mobile station, and a base station controller (BSC) which controls the base station disposed in the preset service area.
Under the above configuration of the cellular telephone system, if a user of the mobile terminal is in conversation with a called or calling party during movement, the service area of the current cell is moved to that of another cell. At the time, when the user of the mobile terminal is adjacent to inter-cell boundary location, the mobile terminal executes handoff to maintain a good conversation quality. That is, when the strength of the signal transmitted from the current base station is weak, the mobile terminal changes its communication link to an adjacent base station which can provide a good quality of signal, without dropping call. For this end, the mobile terminal determines a signal quality of the adjacent other base station, during conversation and provides the determined result to its base station. At this time, the base station receives the determined result from the mobile terminal and if it is determined that the handoff is necessary, transmits a handoff request signal to the mobile station. This procedure is called xe2x80x9ca mobile terminal-assisted handoffxe2x80x9d.
In the handoff execution process, it is important that the mobile terminal accurately receives the signal from the adjacent other base station and provides the received signal to a corresponding base station. For this end, a mobile terminal in the conventional CDMA cellular telephone system includes an RF receiver for demodulating data transmitted from the base station and an additional digital receiver as a searcher for searching different frequencies existing within the same channel. Therefore, the mobile terminal can measure the strength of signal provided from other base station, during conversation, by using the additional searcher.
In a real cellular telephone system, if the service area of one cell is small, the capacity of the mobile terminal within the corresponding service area can be increased. Under the above condition, however, in the case where the user of the mobile terminal is moved at a high speed by using transportation means such as vehicles, the base station and the mobile station are likely to fail in processing the call generated by the handoff.
To facilitate a successful handoff process within the mobile terminal which is moved at a fast speed, firstly, the whole cell area is divided into a plurality of micro-cells, and secondly, above the micro-cells a plurality of macro-cells are disposed, each of which has a larger service area than the micro-cell. Such the division of cells forms a hierarchical cell structure or a layered cell structure. Under the above cell structure, in the case where an arbitrary mobile terminal moves within the micro-cell or to an adjacent macro-cell deviated from the micro-cell, the handoff should be implemented all in the movement within the micro-cell or to the adjacent macro-cell.
In the hierarchical cell structure as mentioned above, since the strength of signal of the base station within the macro-cell is relatively great larger than that within the micro-cell, it is difficult to at the same time use the frequencies of the macro-cell and the micro-cell in the CDMA cellular telephone system. To build the hierarchical cell structure in the CDMA cellular telephone system, inter-frequency handoff between base stations should be executed.
The conventional mobile terminal includes an additional RF receiver for controlling the inter-frequency handoff. In the case where the mobile terminal is comprised of two or more RF receivers, however, light and tiny mobile terminal can not be produced. It is therefore known that the installation of two or more RF receiver in the mobile terminal is impossible, because it may decrease competitiveness of the mobile terminal.
As widely used, there is presented the technology that the mobile terminal including a single RF receiver transmits/receives data to/from the base station and at the same time senses the frequency of other base station to thereby implement the handoff. In other words, in case of transmitting a data frame from the base station to the mobile terminal, the data frame is broken to search the frequency of other base station. In this case, however, there occur problems that a quality of sound information supplied from the base station may be deteriorated and because of the damage of the data frame, control data necessary during conversation can be accordingly damaged. This results in the generation of call drop phenomenon between the mobile terminal and the base station.
Accordingly, the present invention is directed to an inter-frequency handoff execution method and apparatus in a mobile communication system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the invention is to provide an inter-frequency handoff execution method and apparatus in a mobile communication system which inserts a frequency search section into a data frame used as data transmission section during a mobile terminal is in communication with a corresponding base station, executing data transmission in the data transmission section, searching a frequency of other base station in the frequency search section, and executing handoff at a rapid speed without generation of call drop, if execution of the handoff is requested.
According to an aspect of the present invention, an inter-frequency handoff execution method includes the steps of: transmitting from a base station a data frame in which a data transmission section and a frequency search section exist to an arbitrary mobile terminal; executing data transmission in the data transmission section; searching a frequency of other base station in the frequency search section; and determining whether or not handoff is executed in accordance with the searched result.
According to another aspect of the present invention, an inter-frequency handoff execution method includes the steps of: transmitting from an arbitrary mobile terminal a data frame in which a data transmission section and a frequency search section exist to a corresponding base station; executing data transmission in the data transmission section; and transmitting a reverse link pilot signal and a preamble signal in the frequency search section.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.